Fix pull request update showing too many commits with multiple branches (#22856)

When the base repository contains multiple branches with the same
commits as the base branch, pull requests can show a long list of
commits already in the base branch as having been added.

What this is supposed to do is exclude commits already in the base
branch. But the mechansim to do so assumed a commit only exists in a
single branch. Now use `git rev-list A B --not branchName` instead of
filtering commits afterwards.

The logic to detect if there was a force push also was wrong for
multiple branches. If the old commit existed in any branch in the base
repository it would assume there was no force push. Instead check if the
old commit is an ancestor of the new commit.

5 files changed, 49 insertions, 99 deletions

diff --git a/modules/git/commit.go b/modules/git/commit.go
index 4a55645d30..6e8fcb3e08 100644
--- a/modules/git/commit.go
+++ b/modules/git/commit.go
@@ -218,6 +218,19 @@ func (c *Commit) HasPreviousCommit(commitHash SHA1) (bool, error) {
 	return false, err
 }
 
+// IsForcePush returns true if a push from oldCommitHash to this is a force push
+func (c *Commit) IsForcePush(oldCommitID string) (bool, error) {
+	if oldCommitID == EmptySHA {
+		return false, nil
+	}
+	oldCommit, err := c.repo.GetCommit(oldCommitID)
+	if err != nil {
+		return false, err
+	}
+	hasPreviousCommit, err := c.HasPreviousCommit(oldCommit.ID)
+	return !hasPreviousCommit, err
+}
+
 // CommitsBeforeLimit returns num commits before current revision
 func (c *Commit) CommitsBeforeLimit(num int) ([]*Commit, error) {
 	return c.repo.getCommitsBeforeLimit(c.ID, num)
diff --git a/modules/git/repo_commit.go b/modules/git/repo_commit.go
index a62e0670fe..0e1b00ce08 100644
--- a/modules/git/repo_commit.go
+++ b/modules/git/repo_commit.go
@@ -323,6 +323,27 @@ func (repo *Repository) CommitsBetweenLimit(last, before *Commit, limit, skip in
 	return repo.parsePrettyFormatLogToList(bytes.TrimSpace(stdout))
 }
 
+// CommitsBetweenNotBase returns a list that contains commits between [before, last), excluding commits in baseBranch.
+// If before is detached (removed by reset + push) it is not included.
+func (repo *Repository) CommitsBetweenNotBase(last, before *Commit, baseBranch string) ([]*Commit, error) {
+	var stdout []byte
+	var err error
+	if before == nil {
+		stdout, _, err = NewCommand(repo.Ctx, "rev-list").AddDynamicArguments(last.ID.String()).AddOptionValues("--not", baseBranch).RunStdBytes(&RunOpts{Dir: repo.Path})
+	} else {
+		stdout, _, err = NewCommand(repo.Ctx, "rev-list").AddDynamicArguments(before.ID.String()+".."+last.ID.String()).AddOptionValues("--not", baseBranch).RunStdBytes(&RunOpts{Dir: repo.Path})
+		if err != nil && strings.Contains(err.Error(), "no merge base") {
+			// future versions of git >= 2.28 are likely to return an error if before and last have become unrelated.
+			// previously it would return the results of git rev-list before last so let's try that...
+			stdout, _, err = NewCommand(repo.Ctx, "rev-list").AddDynamicArguments(before.ID.String(), last.ID.String()).AddOptionValues("--not", baseBranch).RunStdBytes(&RunOpts{Dir: repo.Path})
+		}
+	}
+	if err != nil {
+		return nil, err
+	}
+	return repo.parsePrettyFormatLogToList(bytes.TrimSpace(stdout))
+}
+
 // CommitsBetweenIDs return commits between twoe commits
 func (repo *Repository) CommitsBetweenIDs(last, before string) ([]*Commit, error) {
 	lastCommit, err := repo.GetCommit(last)
diff --git a/modules/repository/push.go b/modules/repository/push.go
index 1fa711b359..aa1552351d 100644
--- a/modules/repository/push.go
+++ b/modules/repository/push.go
@@ -4,10 +4,8 @@
 package repository
 
 import (
-	"context"
 	"strings"
 
-	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/modules/git"
 )
 
@@ -96,19 +94,3 @@ func (opts *PushUpdateOptions) RefName() string {
 func (opts *PushUpdateOptions) RepoFullName() string {
 	return opts.RepoUserName + "/" + opts.RepoName
 }
-
-// IsForcePush detect if a push is a force push
-func IsForcePush(ctx context.Context, opts *PushUpdateOptions) (bool, error) {
-	if !opts.IsUpdateBranch() {
-		return false, nil
-	}
-
-	output, _, err := git.NewCommand(ctx, "rev-list", "--max-count=1").AddDynamicArguments(opts.OldCommitID, "^"+opts.NewCommitID).
-		RunStdString(&git.RunOpts{Dir: repo_model.RepoPath(opts.RepoUserName, opts.RepoName)})
-	if err != nil {
-		return false, err
-	} else if len(output) > 0 {
-		return true, nil
-	}
-	return false, nil
-}
diff --git a/services/pull/comment.go b/services/pull/comment.go
index 068aca6cd1..933ad09a85 100644
--- a/services/pull/comment.go
+++ b/services/pull/comment.go
@@ -14,58 +14,6 @@ import (
 	issue_service "code.gitea.io/gitea/services/issue"
 )
 
-type commitBranchCheckItem struct {
-	Commit  *git.Commit
-	Checked bool
-}
-
-func commitBranchCheck(gitRepo *git.Repository, startCommit *git.Commit, endCommitID, baseBranch string, commitList map[string]*commitBranchCheckItem) error {
-	if startCommit.ID.String() == endCommitID {
-		return nil
-	}
-
-	checkStack := make([]string, 0, 10)
-	checkStack = append(checkStack, startCommit.ID.String())
-
-	for len(checkStack) > 0 {
-		commitID := checkStack[0]
-		checkStack = checkStack[1:]
-
-		item, ok := commitList[commitID]
-		if !ok {
-			continue
-		}
-
-		if item.Commit.ID.String() == endCommitID {
-			continue
-		}
-
-		if err := item.Commit.LoadBranchName(); err != nil {
-			return err
-		}
-
-		if item.Commit.Branch == baseBranch {
-			continue
-		}
-
-		if item.Checked {
-			continue
-		}
-
-		item.Checked = true
-
-		parentNum := item.Commit.ParentCount()
-		for i := 0; i < parentNum; i++ {
-			parentCommit, err := item.Commit.Parent(i)
-			if err != nil {
-				return err
-			}
-			checkStack = append(checkStack, parentCommit.ID.String())
-		}
-	}
-	return nil
-}
-
 // getCommitIDsFromRepo get commit IDs from repo in between oldCommitID and newCommitID
 // isForcePush will be true if oldCommit isn't on the branch
 // Commit on baseBranch will skip
@@ -82,47 +30,33 @@ func getCommitIDsFromRepo(ctx context.Context, repo *repo_model.Repository, oldC
 		return nil, false, err
 	}
 
-	if err = oldCommit.LoadBranchName(); err != nil {
-		return nil, false, err
-	}
-
-	if len(oldCommit.Branch) == 0 {
-		commitIDs = make([]string, 2)
-		commitIDs[0] = oldCommitID
-		commitIDs[1] = newCommitID
-
-		return commitIDs, true, err
-	}
-
 	newCommit, err := gitRepo.GetCommit(newCommitID)
 	if err != nil {
 		return nil, false, err
 	}
 
-	commits, err := newCommit.CommitsBeforeUntil(oldCommitID)
+	isForcePush, err = newCommit.IsForcePush(oldCommitID)
 	if err != nil {
 		return nil, false, err
 	}
 
-	commitIDs = make([]string, 0, len(commits))
-	commitChecks := make(map[string]*commitBranchCheckItem)
+	if isForcePush {
+		commitIDs = make([]string, 2)
+		commitIDs[0] = oldCommitID
+		commitIDs[1] = newCommitID
 
-	for _, commit := range commits {
-		commitChecks[commit.ID.String()] = &commitBranchCheckItem{
-			Commit:  commit,
-			Checked: false,
-		}
+		return commitIDs, isForcePush, err
 	}
 
-	if err = commitBranchCheck(gitRepo, newCommit, oldCommitID, baseBranch, commitChecks); err != nil {
-		return
+	// Find commits between new and old commit exclusing base branch commits
+	commits, err := gitRepo.CommitsBetweenNotBase(newCommit, oldCommit, baseBranch)
+	if err != nil {
+		return nil, false, err
 	}
 
+	commitIDs = make([]string, 0, len(commits))
 	for i := len(commits) - 1; i >= 0; i-- {
-		commitID := commits[i].ID.String()
-		if item, ok := commitChecks[commitID]; ok && item.Checked {
-			commitIDs = append(commitIDs, commitID)
-		}
+		commitIDs = append(commitIDs, commits[i].ID.String())
 	}
 
 	return commitIDs, isForcePush, err
diff --git a/services/repository/push.go b/services/repository/push.go
index cdf030396f..4b574e3440 100644
--- a/services/repository/push.go
+++ b/services/repository/push.go
@@ -206,12 +206,12 @@ func pushUpdates(optsList []*repo_module.PushUpdateOptions) error {
 						return fmt.Errorf("newCommit.CommitsBeforeUntil: %w", err)
 					}
 
-					isForce, err := repo_module.IsForcePush(ctx, opts)
+					isForcePush, err := newCommit.IsForcePush(opts.OldCommitID)
 					if err != nil {
-						log.Error("isForcePush %s:%s failed: %v", repo.FullName(), branch, err)
+						log.Error("IsForcePush %s:%s failed: %v", repo.FullName(), branch, err)
 					}
 
-					if isForce {
+					if isForcePush {
 						log.Trace("Push %s is a force push", opts.NewCommitID)
 
 						cache.Remove(repo.GetCommitsCountCacheKey(opts.RefName(), true))